A document seen by the Guardian indicated around 80 police officers used the identities of dead children between 1968 and 1994, the paper reported.
The practice was allegedly adopted to lend credibility to officers working undercover and provide them with a back story while spying.
More top news
The Gallagher brothers have had a turbulent relationship since Oasis fell apart in 2009.
Choir wins public vote, while judges pick dancers ahead of 12-year-old singer-songwriter Henry Gallagher.
The hunt for murder suspect Jed Allen has ended after police found his body two days after discovering his mother, stepdad and sister dead.